Self-ballasted compact fluorescent lamps are highly efficient replacements for incandescent lamps. While their initial costs are somewhat higher than the incandescent lamps they are designed to replace, their greater efficacy and longer life make them practical.
Unlike the incandescent lamps they replace, which cease operation immediately upon failure of the filament, compact fluorescent lamps experience end-of-life failure when the filaments of the lamp have depleted their emissive material. Under these conditions the electronic ballast can continue to operate the lamp and dissipate considerable power. This power dissipation can cause localized heating of the glass lamp envelope in the vicinity of the cathode, causing the plastic housing of the ballast to melt.
Increasing the space between the lamp envelope and the wall of the ballast housing is not practical since safety standards for self-ballasted compact fluorescent lamps limit the amount of space between the glass lamp tube and the plastic housing to minimize electrical shock hazards.